1. Field of the Invention
The present invention relates to a resin welded body in which a resin part that transmits laser light with a predetermined wavelength and a resin part that absorbs laser light with the same wavelength are joined by welding using the laser light.
2. Description of the Related Art
Conventionally, a laser light welding method is used for manufacturing a resin welded body. The laser light welding method is briefly described below. First, a portion of a first resin part that transmits laser light with a predetermined wavelength is caused to abut a portion of a second resin part that absorbs laser light with the same wavelength. Then, the laser light is applied to the abutting surfaces from the first resin part side. Then, the laser light transmits the first resin part and is absorbed at around the surface of the second resin part. The energy of the absorbed laser light is converted to heat that heats the surface of the second resin part. This forms a melted portion on the abutting surfaces of the first resin part and the second resin part to be welded.
In this welding process, the surface adhesion property of the abutting surfaces, which will be a joining portion, of the both resin parts is a key. When the surface adhesion property is insufficient, the heat transfer from the second resin part to the first resin part becomes insufficient, leading to joining failure. Thus, in order to improve the surface adhesion property between the both resin parts, the laser light is applied with the abutting surfaces pressurized from the outside to be abutted. Note that, when the resin welded body is a closed container, a ring-shaped sealing member is placed on the inner side of a joining portion that is formed in a circumferential shape.
On the other hand, in the melted portion, melting progresses unless application of the laser light is stopped or pressurization from the outside is stopped. As a result of the progress of melting, the clearance between the both resin parts is reduced due to the sinking of the joining portion. In order to precisely manage the amount of sinking of the joining portion, Patent Document 1 discloses that a stopper (protrusion) is provided on one of the both resin parts to limit the amount of sinking of the joining portion.
According to the Patent Document 1, all of the joining portion, stopper and sealing member are placed in a circumferential shape, and the interference (squeeze) of the sealing member is determined based on the amount of sinking limited by the stopper. Furthermore, the joining portion, stopper and sealing member are placed in this order from the outer circumference side, which allows the interference of the sealing member to be determined only from the dimension of the stopper even when bending occurs in the joining portion due to variation in melting condition, maintaining stable sealing capability.    [Patent Document 1] JP-B-4531074
According to the Patent Document 1, a key for achieving precise dimensional management is to cause the stopper to reliably abut an opposite resin part. On the other hand, surface pressure obtained by compressing the sealing member generates a reaction force in the direction of preventing the both resin parts from abutting each other. So, in order to cause the stopper to reliably abut the opposite surface, an area to be pressurized needs to be on the inner circumference side with respect to the stopper.
However, when the laser light is applied to the joining portion along the circumference, if the area to be pressurized is set to the inner circumference side with respect to the laser light path, a pressurization jig or a part for supporting the jig may break the laser light path. Because of this, the pressurization jig needs to be made of a material that does not absorb the laser light (e.g. glass). However, even a glass jig may pose a problem that reduces laser energy due to reflection.
Furthermore, adhesion foreign matter to the glass jig or clouding of the glass jig due to gas generated from melted resin may also contribute to reduction in laser energy. This requires frequent maintenance of the glass jig, which reduces productivity.